Porous carbons

ABSTRACT

A method is provided for making mesoporous resin. It comprises: (a) providing a nucleophilic component which comprises a phenolic compound or a phenol condensation prepolymer optionally with one or more modifying reagents selected from hydroquinone, resorcinol, urea, aromatic amines and heteroaromatic amines; (b) dissolving the nucleophilic component in a pore former selected from the group consisting of a diol, a diol ether, a cyclic ester, a substituted cyclic ester, a substituted linear amide, a substituted cyclic amide, an amino alcohol and a mixture of any of the above with water, together with at least one electrophilic cross-linking agent selected from the group consisting of formaldehyde, paraformaldehyde, furfural and hexamethylene tetramine; and (c) condensing the nucleophilic component and the electrophilic cross-linking agent in the presence of the pore former to form a porous resin. The resin may be formed in situ by pouring the partially cross-linked resin into hot oil. Mesoporous resin beads are obtained which can be carbonised into mesoporous carbon beads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/344248 filed 29 May 2003 now pending, which was derived fromInternational Application No. PCT/GB01/03560 filed 7 Aug. 2001. Theentire disclosures of these earlier related applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to improved phenolic resin structureswhich can be used as ion exchange resins and can be used to prepareporous carbon materials and to a methods for making these.

BACKGROUND TO THE INVENTION

Sulphonated phenolic resins were first used as ion exchange resins inthe 1930's (Adams et al, J Soc Chem Ind. 54, (1935) 1-GT) and relativelystable cation and anion exchange resins were used extensively for thesoftening and demineralisation of water. Other phenolic based resinsinclude the weak base anion exchange resins that have been primarilyused in food processing applications (Cristal M J, Chem and Ind, 814,(1983) Nov. 7) and chelation resins which can be produced to giveremarkable selectivity for the adsorption of metal ions such as cesium(U.S. Pat. No. 4,423,159, 1983 and U.S. Pat. No. 5,441,991, 1995). Theion exchange powders, can be produced by either bulk curing of the resinfollowed by milling (e.g. WO91/09891) to produce a low porosity powderor by reversed phase condensation (Unitaka Ltd U.S. Pat. No. 4,576,9691986). One of the limitations of these materials was limited internalporosity and they were rapidly replaced by the highly porous sulphonatedstyrene divinyl benzene copolymer based ion exchange resins when thesebecame available. However, although the phenolic based resins havelargely disappeared, specific applications do still exist in foodrelated industries based on their underlying performancecharacteristics.

The phenolic resins can be carbonised to form mesoporous carbons.Mesoporous carbons are used as adsorbents or catalysts supports and canbe used in spherical, granular of thin film form. Existing productionmethods use gas phase and chemical activation routes to producemesoporous carbons but, activated carbon, as conventionally produced, isnormally microporous (<2 nm pore diameter—IUPAC definition) with littleor no pore volume in the mesopore (2-50 nm) and macropore (>50 nm)range. For some critical adsorption processes such as evaporativeemission control, and when used as a catalyst support, particularly inliquid phase applications, this is a major drawback.

Conventional activated carbons can be made mesoporous through severeactivation but this seriously degrades their mechanical properties andthe materials are generally then only available as fine powders. U.S.Pat. No. 4,677,086 discloses the use of chemical activation to producemesoporous carbons without such severe mechanical degradation and whichalso can be produced as extrudates. These are however still produced aspowders and must then be bound to produce, for instance, extrudate foruse in fixed bed gas phase processes. In most cases the binders that canbe used are polymeric or ceramic which then restricts the conditionsunder which the carbons can be used.

Chemical activation can also be used to directly produce mesoporouscarbons by pelleting or extruding a plasticised acidic lignin base charand then directly carbonising and activating the mixture as disclosed inU.S. Pat. No. 5,324,703. The production route also leads to a lowmacroporosity, which can have disadvantages in catalytic and liquidphase processes. The route also has the disadvantage of requiringcompounds such as phosphoric acid and zinc chloride as the activatingagents, which can cause severe environmental problems and have a majorimpact on the materials of construction of the process plant.

An alternative route is to carbonise sulphonated styrene—divinylbenzeneco-polymers as disclosed in U.S. Pat. No. 4,040,990 and U.S. Pat. No.4,839,331. These produce carbons directly by pyrolysis withmeso/microporosity without recourse to further activation. The materialstherefore have good mechanical properties. They are, however, limited torelatively small particle sizes, fixed by the polymer production route,and have a limited range of mesopore structures. They are also veryexpensive reflecting the high cost of the precursor polymer, the lowcarbon yields and environmental problems associated with processingpolymers containing large amounts of sulphur. The resultant carbons arealso contaminated with sulphur, which restricts their use as catalystssupports.

A further route has also been disclosed in U.S. Pat. No. 5,977,016whereby sulphonated styrene—divinylbenzene co-polymer particles can beformed into pellets in the presence of large volume of concentratedsulphuric acid and then carbonised to give structured materials withboth meso- and macroporosity. The route is however complex and expensivewith significant environmental problems

A further route is disclosed in U.S. Pat. No. 4,263,268 where amesoporous silica with the desired macroshape (i.e. spheres) isimpregnated with a carbon forming polymer, such as phenolic orpolyfurfuryl resin and then dissolving the silica template in an alkali.This again is a highly expensive route and is only capable of producingthe carbon material in a limited range of shapes and forms

SUMMARY OF THE INVENTION

We have now devised an improved method of producing porous resinstructures which can be used to form porous carbons such as mesoporouscarbon without, gas phase or chemical activation.

According to the invention there is provided a method for forming aporous resin structure which method comprises the condensation of anucleophilic component with an electrophilic cross-linking agents insolution in the presence of a pore former.

The condensation can be catalysed or non catalysed.

The invention also provides a method for forming a porous carbonstructure in which the porous resin is carbonised to form the porouscarbon structure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 shows pore former content in the resin composition on theporosity of derived carbonized material with reaction systemPhenol-Formaldehyde-Ethylene Glycol-Sulphuric Acid;

FIG. 2 shows the effect of aniline content in resin composition of thereaction system Phenol-Aniline-Formaldehyde-Ethylene Glycol-SuphuricAcid on the porosity of derived carbons;

FIG. 3 a shows the effect of the pore former content on the porosity ofphenolic resins with reaction system Novolac-Hexamine-Ethylene Glycol;

FIG. 3 b shows the effect the effect of the pore former in resincomposition on the porosity of corresponding carbonized materials withreaction system Novolac-Hexamine-Ethylene Glycol;

FIG. 4 shows the effect of additions of Aniline or Urea to the resincompositions of Novolac-Hexamine-Ethylene Glycol reaction system on theporosity of resulting carbons;

FIG. 5 shows the effect of the nature of the pore former on the porosityof the carbons derived from the resins of reaction systems Novolac-PoreFormer-Hexamine;

FIG. 6 shows the effect of the pore former modification with anothersolvents in the resin compositions based on Novolac and Hexamine on theporosity of derived carbon;

FIG. 7 shows the effect of carbonization procedure on the porosity ofcarbons derived from copper-containing resin;

FIG. 8 shows the effect of resin cross-linking conditions on theporosity of derived carbons;

FIG. 9 shows porosity of carbon derived from the resin ofNovolac-Hexamine-Furfural-Ethylene Glycol reaction system;

FIG. 10 shows porosity parameters of the resin prepared in block(Novolac-Hexamine-Ethylene Glycol reaction system) and derived carbon;

FIG. 11 shows the effect of different processing of the resin ofNovolac-Hexamine-Ethylene Glycol-Boric Acid reaction system on theporosity of derived carbons;

FIG. 12 a shows the effect of Ethylene Glycol content in block resincomposition on the porosity of the resin, reaction systemNovolac-Melamine-Formaldehyde-Ethylene Glycol;

FIG. 12 b shows the effect of the EG content in the composition of theresins prepared in blocks and of the reaction systemNovolac-Melamine-Formaldehyde-Ethylene Glycol on the porosity of derivedcarbons; and

FIG. 13 shows a comparison of porosity of carbons derived from thereaction systems Novolac-Hexamine-Ethylene Glycol,Novolac-Resorcinol-Hexamine-Ethylene Glycol andNovolac-Hydroquinone-Hexamine-Ethylglycol.

DESCRIPTION OF PREFERRED FEATURES

The nucleophilic component can be for example phenol, aphenolformaldehyde pre-polymer—a Novolac optionally together with amodifying agent.

The electrophilic component can be for example formaldehyde, hexamine,furfural.

Preferably the pore former acts as the solvent.

Methods for preparation of the porous polycondensation resins generallycomprise dissolving nucleophilic components (e.g. phenol, Novolac,modifying reagents) and electrophilic cross-linking components (e.g.formaldehyde, hexamine, furfural) in the pore former with or withoutcatalysts (acidic or basic) and thermosetting the solution obtained toproduce cured, solid, insoluble and infusible resins with the poreformer evenly distributed within the resin matrix creating pores ofcontrolled size.

The invention is particularly useful for producing porous carbons whichcan be carbonised to mesoporous/macroporous carbons. By mesoporouscarbon we mean here a carbon possessing alongside micropores, pores withdiameter from ca. 2 nm to ca. 50 nm and by macroporous a carbonpossessing alongside micropores pores with diameters larger than 50 nm,as measured by nitrogen adsorption and mercury porosimetry methods andas defined by IUPAC.

Phenol Polycondensation Pre-polymer

The phenolformaldehyde condensation pre-polymer can be a Novolac resin.Novolac resins are typically produced by the acid catalysed condensationof phenol and formaldehyde in approximately equimolar amounts. Novolacsare usually thermoplastic solid polymers that melt at or above 100° C.depending on the average molecular weight. They are essentially linearchains with molecular weights of from 500 to 2000 D, where phenolicmoieties are linked with methylene (predominantly) and methylene etherbridges and possess one nucleophilic active site, predominantly in theunsubstituted ortho-position to hydroxyl group. There can be alsovarying degrees of chain branching depending upon the productionconditions.

Whilst the commercial materials are largely produced using phenol andformaldehyde, a variety of modifying reagents can be used at thepre-polymer formation stage to introduce a range of different oxygen andnitrogen functionality's and cross-linking sites. These include but arenot limited to:

1. Hydroquinone and resorcinol. Both are more reactive than phenol andcan lead to some cross-linking at the pre-polymer production stage. Itis also possible to introduce these compounds at the cross-linking stageto provide different cross-linking paths. These also increase the oxygenfunctionality of the resins.

2. Nitrogen containing compounds that are active in polycondensationreactions, such as urea, aromatic (aniline) and heteroaromatic(melamine) amines. These allow the introduction of specific types ofnitrogen functionality into the initial polymer (and final carbon) andinfluence the development of the mesoporous structure of both the resinsand the final carbons.

Like hydroquinone and resorcinol, all the nitrogen containingnucleophilic modifying reagents which can be used in the presentinvention possess two and more active sites and are more reactive incondensation reactions than phenol or Novolacs. It means that they arefirst to react with primary cross-linking agents forming secondarycross-linking agents in situ. In the case of melamine it is preferableto prepare the secondary cross-linking agent—hydroxymethylatedmelamine—in advance.

Novolacs are thermally stable in that they can be heated and cooledrepeatedly without structural change. They are cured on addition ofcross-linking agents and heating.

The process of the invention is carried out in solution and the poreformer can also be the solvent. For example a solution, obtained fromcommercial Novolac pre-polymers together with modifying reagents (ifrequired), cross-linking agents and catalysts (if required) and anappropriate amount of the pore former as a solvent, is heated to bringabout the cross-linking reaction, resulting in a solid resin.

Alternatively the solid porous polycondensation resins which can be usedin the invention can be produced directly from phenol (and optionallymodifying agents) and formaldehyde (or other cross-linking agents) onheating their solution in the pore former with the catalyst (acidic orbasic).

In both cases the reaction solution will set during the cross-linkingreaction if the correct composition is used “locking” the pore formerinto the resin structure and creating a mesoporous resin.

The-porous resin precursor can be cast into a block and comminuted togive a powder of particle size in the range of 1 to 1000 microns. Thisresin powder can then be carbonised to give a porous carbon with a poresize which can be controlled e.g. to give a mean pore size of between 2and 50 nm (mesopores) or greater than 50 nm (macropores) and also withmicropores with a mean pore size between 0.6 and 2 nm.

If the viscous solution of the partially cross-linked pre-polymer ispoured into a hot liquid such as mineral oil containing a dispersingagent and the mixture stirred, the pre-polymer solution will form intobeads. These are initially liquid and then, as curing proceeds, theybecome solid. The average bead particle size is controlled by severalprocess parameters including the stirrer type and speed, the oiltemperature and viscosity, the pre-polymer solution viscosity and volumeratio of the solution to the oil and can be adjusted between 5 and 2000microns. These beads can then be filtered off from the oil and, afterpore former removal, pyrolysed to give meso- or macroporous carbonbeads.

It is thought that the mechanism of mesopore generation is due to aphase separation process that occurs during the cross-linking reaction.In the absence of a pore former, as the linear chains of pre-polymerundergo cross-linking, the molecular weight initially increases.Residual low molecular weight components become insoluble in the highermolecular weight regions causing a phase separation into cross-linkedhigh molecular weight domains within the lower molecular weightcontinuous phase. Further condensation of light components to theoutside of the growing domains occurs until the cross-linked phasebecomes essentially continuous with residual lighter pre-polymer trappedbetween the domains.

Pore Formers

There are a large number of solvents that can be employed as the poreformers. The key requirements for these solvents are: highsolubility/compatibility of the reaction components in the solvent;useable viscosity of the pre-polymer/cross-linking agent/solventsolution (this for instance essentially rules out glycerol which givesan unacceptably high viscosity); reasonably high boiling temperature toperform the polycondensation reaction at a reasonable rate withoutsignificant solvent evaporation.

Pore formers which can be used include but are not limited to: ethyleneglycol, 1,4-butylene glycol (diols); diethylene glycol, triethyleneglycol (diols-ethers); gamma-butyrolactone, propylene carbonate (cyclicesters); dimethylformamide, N-methyl-2-pyrrolidinone (substitutedamides, cyclic and linear); monoethanolamine (aminoalcohol).

In the presence of a low level of pore former the pore former iscompatible with, and remains within, the cross-linked resin domains,(e.g., <120 parts/100 parts Novolac for the Novolac-Hexamine-EthyleneGlycol reaction system), whilst the remainder forms a solution with thepartially cross-linked polymer between the domains. In the presence ofhigher levels of pore former, which exceed the capacity of thecross-linked resin, the pore former adds to the light polymer fractionincreasing the volume of material in the voids between the domains thatgives rise to the mesoporosity. In general, the higher the pore formercontent, the wider micropores and the higher the pore volume.

This phase separation mechanism then provides a variety of ways ofcontrolling the pore development in the cross-linked resin structures.These are: chemical composition and concentration of the pore former;chemical composition and quantity of the cross-linking electrophilicagents, presence, chemical nature and concentration of modifyingnucleophilic agents, chemical composition of phenolic nucleophiliccomponents (phenol, Novolac), presence, chemical nature (acidic, basic)and concentration of the catalyst.

To produce the spherical resins by the oil dispersion method referred toabove the solvent should also be incompatible with the oil andcompatible with water in order to secure the formation of a “water inoil” type emulsion with the beads of the resin solution dispersed in thebulk of the oil, minimise the solvent extraction into the oil andproblems with its recovery and enhance simple recovery of the solventfrom the solid resin beads by washing with water

Both protogenic and aprotic solvents of different classes of organiccompounds match these requirements and can be used as pore formers, bothindividually, in mixtures or mixed with water.

Different solvents, though quite similar in structure, will havedifferent compatibilities with the cross-linked resin. This will thenalter the phase separation to varying extents and will then affect theporosity of resins and corresponding carbons. Deliberate addition ofwater to these polar organic solvents will decrease the compatibility ofthe resin and the resultant pore former, which could be beneficial forsome reaction systems, though water, as one of the reaction products, isinevitably present in any reaction where a carbonylic compound is usedas the cross-linking agent.

The common feature of amides as the pore formers is that they normallyrequire deliberate addition of water (2-5%) to promote cross-linkingwith hexamine. When amides are used as the pore formers the finalcarbons exhibit no mesoporosity detectable by nitrogen adsorption, butthey are of relatively low bulk density, which clearly indicates thepresence of big pores (>50 nm).

Some pore formers, under special conditions, are also able to contributeto the cross-linking process. For example, active carbocations can beformed from ethylene glycol in strong acidic media or the methylolderivatives of monoethanolamine and formamide with formaldehyde, whichwill react as secondary cross-linking agents.

Cross-Linking Agents

The primary cross-linking agents used in the invention are formaldehyde,furfural and hexamethylenetetramine (hexamine). Formaldehyde isintroduced either in solution in the pore former or as solidparaformaldehyde, (CH₂O)_(x). Formaldehyde cross-links phenolic moietiesforming —CH₂— and —CH₂—O—CH₂— bridges at ratios depending on the pH ofthe reaction mixture. Methylene bridges are the only ones formed instrong acidic and strong alkali media, whereas at pH's close to neutraleither type of bridges appear. Water is formed as the stoichiometricsecondary condensation product at a level depending on the type ofbridge formed. 1 mole per mole of formaldehyde in the case of themethylene bridges or 1 mole H₂O per 2 moles CH₂O in the case of theether bridges. The “condensation” water may then influence the phaseseparation and mesopore formation process by reducing the compatibilityof the water containing pore former with the resin domain depending onthe pore forming solvent being used.

Complete cross-linking of phenol with formaldehyde by methylene bridgesrequires approximately a 1 to 1.5 molar ratio of the reagents. Takinginto account the formation of some ether type bridges, the phenol toformaldehyde molar ratio in the resin compositions of the invention ispreferably maintained at 1.6 to 1.8 level. This requires an additional 9to 12 weight parts of formaldehyde (paraformaldehyde) per 100 weightparts of Novolac resin.

Furfural differs from formaldehyde in that the electrophilic reactivityof its carbonyl group is supplemented by the high nucleophilic activityof the heterocyclic. Moreover, ring scission and consecutive reactionscan give a wide range of products, which can provide additionalcross-linking paths, possibly involving phenolic hydroxyls. These aretypical for furan resin derivatives, especially in acidic media and, incombination with other cross linking agents, provide an additional routeto modify both the chemical structure and porosity of the resins.

Hexamine can be introduced as a powder directly into the reactionsolution. On heating ring cleavage occurs, catalysed by traces of waterand, possibly, protonic solvents, resulting in the formation of theactive species—aminocarbinols. On cross-linking these form differentbridges, including simple methylene and more complex—nitrogen-containinggroupings like bis-methylene amine, tris-methylene amine and1,3-oxazine. The low molecular weight condensation by-products arewater, that then cleaves the next portion of hexamine, and ammonia.Ammonia, though highly volatile at the reaction conditions, increasesthe pH of the reaction solution when no acidic or basic catalysts arepresent, which may also affect the phase separation and mesoporeformation process.

In the present invention hexamine is preferably used for cross-linkingNovolac resin at a concentration of 9 weight parts hexamine per 100weight parts of Novolac. This ensures the formation of the solid resinwith maximal cross-linking degree. This is in contrast to previouslydisclosed sintered resin structures where typically up to 3 parts ofhexamine per 100 parts of Novolac were used (EP 0245551). When hexamineis used in the ethylene glycol solution at a level of 3 weight parts per100 weight parts of Novolac only non-porous semi-solid rubbery materialis obtained, whereas at 9 weight parts level a highly mesoporous andsolid resin is produced. It is thought that ethylene glycol might act asan internal plasticizer when the cross-linking degree is not adequate.

Modifying Agents

Most of the modifying agents which can be used in the invention containnitrogen thus introducing this into the resins and therefore the finalcarbons. Their common feature is their reactivity in condensationreactions, which is higher than that of phenol and Novolac resin. Thereare at least three distinct ways in which these compounds participate inthe condensation process when added in relatively small amounts (5-30weight % of the phenolic component):

1. Novolac—primary cross-linking agent—modifying agent reaction system.Here the modifying agent reacts rapidly with the primary cross-linkingagent forming a secondary cross-linking agent that then binds theNovolac chains together. As a result the resin consists of homocondensedphenolformaldehyde chains bridged with nitrogen-containing groupings (orresorcinol or hydroquinone derived moieties).

2. Phenol—cross-linking agent—modifying agent—strong acidic or strongbasic catalyst. Separate homocondensation processes occur for the twodifferent nucleophilic reagents (phenol and modifying agent). This thenresults in the formation of a binary resin matrixes where the two resincomponents behave in a different way on thermal treatment.

3. Phenol—cross-linking agent—modifying agent—weak acidic or weak basiccatalysts, or no catalyst at all. This leads to a co-condensationprocess with formation of structurally homogeneous material withmodifying moieties evenly distributed within phenolic resin.

For the three different cases the effect of the modifying agent on theporosity of both resin produced and final carbon can be different. Thus,for the reaction system phenol—aniline—formaldehyde—ethyleneglycol—sulphuric acid (strong acid as a catalyst) increasing the amountof aniline from 0 to 20 mol. % relative to the phenol leads to a gradualnarrowing of mesopores. Conversely in the case ofNovolac—aniline—hexamine—ethylene glycol andNovolac—aniline—formaldehyde—ethylene glycol reaction systems (nocatalyst at all) increasing the amount of aniline from 0 to 20 weight %relative to the Novolac produces a pronounced increase in both mesoporewidth and volume.

Reaction Rate Effects

Besides pure catalytic effects, such as increasing the reaction rate andchanging the reaction paths, strong acids and alkalis enhancedramatically the solubility and compatibility of growing resin chainsand aggregates in the polar pore former due to phenolate formation (foralkalis) or protonation (for acids). Too high catalyst concentrationscan also result in enhancing some undesirable reactions, such asdecomposition of amide and ester pore formers, disproportionation ofaldehydes (alkali catalysed Cannizzaro reaction), blocking of activesites of benzene rings due to sulphonation (with sulphuric acid as acatalyst). Too low catalyst concentrations can result not only inconsiderable slowing down of condensation reaction, but also in adeterioration of porosity.

The development of mesoporosity within a resin of constant compositionis also dependent upon the rate of the cross-linking reaction. Thecondensation reaction rate can be controlled by the reaction temperatureand also via heat transfer phenomena which are controlled by thephysical form of the resin (block, beads, etc). This is found in thepreparation of the spherical resin, where heat transfer phenomena can beignored because the process is carried out in hot oil with small resindroplets. If the solid cured spherical resin is prepared from a solutionof Novolac and hexamine in ethylene glycol by smoothly increasing thetemperature to 100-105° C. (solution quite close to gel state),dispersing the solution into the oil at about the same temperature, andthen gradually raising the temperature to 150-160° C. to complete thecross-linking a highly mesoporous resin is formed. Conversely, if theNovolac and hexamine are dissolved in ethylene glycol at 65-70° C. anddirectly dispersed into the oil at 160-180° C., the mesoporosity of theresulting cured resin will be dramatically decreased. On carbonisationthe first resin produces highly mesoporous carbon with moderate to lowmicroporosity. The second resin produces carbon with relatively highmicroporosity, but low mesoporosity.

It is thought that, when the cross-linking proceeds very quickly underthe temperature shock conditions, aggregates of relatively small domainsare formed instead of the normal sized domains formed under mild curingconditions. The voids between the small domains in the aggregates thengive rise to additional microporosity. And few voids between theaggregates create some mesoporosity.

It has also been found that the way in which the pore former is removedfrom the cured resin can be important to the generation of the porosityin corresponding carbon. If the pore former (e.g., ethylene glycol) isremoved simply on pyrolysis during the carbon production, themesoporosity may be lost. It has been found that it is preferable toremove the pore former at a low temperature, e.g., below 100° C., viawashing the resin with water or vacuum distillation, with subsequentrecycling of the pore former. The washing (sometimes—afterneutralisation) becomes absolutely necessary, when alkalis or sulphuricacid are used as catalysts. This is because alkalis will affect thecarbonisation process, sometimes in very undesirable way, whereassulphuric acid will contaminate the carbon with sulphur, reducing itsvalue as a catalysts supports.

Other Additions

It has also been found that heteroatoms can be incorporated in the resinstructure. Metals such as copper, nickel, chromium etc, can beincorporated in the porous resin structure by incorporating the metal asa solution of a salt in the pore forming solvent prior to cross linkingthe resin and non metals and metalloids can be incorporated directlyinto the mesoporous resin and thence into the mesoporous carbons. Wherean inorganic compound is soluble in the pore former it can be addeddirectly to the initial reaction solution. The preparation procedure isthen carried out in the usual way. The metal species are then evenlydistributed within the resin matrix. In some cases the ability of theelement to complex with or have some other specific interaction with,the hydroxy- or aminogroups of phenolic resin enhances the initialdistribution to the atomic level. Incorporation of the highly dispersedelement within the resin then leads to a high dispersion of the elementin the carbon formed during pyrolysis.

Carbonisation and Activation

The transformation of the porous resins in any physical form and shapeinto the porous carbons of the invention is performed by carbonisation,i.e. high temperature treatment in an inert atmosphere and attemperatures from −600° C. upwards. The pyrolysis process commences atabout 400° C. and is largely complete by around 700° C. although furthersmall weight losses continue up to around 1400° C. However surface areadevelopment is only significant above around 600° C. at which point thematerial is not strictly carbon. The development of a significantelectrical conductivity is only observed at above 700° C. The inertatmosphere for the pyrolysis can be secured by the appropriate gas flow.Nitrogen and argon can be used as inert purge gases at any temperaturewhilst carbon dioxide is effectively inert up to around 800° C. in theabsence of catalytic metals. Vacuum may also be used although this canlead to the development of molecular sieving behaviour. Due to thepresence of mesopores in these materials, which provide efficient escaperoutes for the volatile products, the heating rates employed can be veryhigh—up to 10° C. per minute. The porosity of the carbons can be furtherenhanced by conventional activation methods, e.g. by activation in steamabove 750° C. or carbon dioxide above 800° C., which can give surfaceareas as measured by BET 5 point method of up to 2000 m²/g. It has beenfound that “physical” activation with carbon dioxide at the temperaturesin the range 850-900° C. gives rise predominantly to microporosity,whereas air activation at 420-450° C. enhances rather mesopore size andvolume e.g. in the same pore size and range as in the original carbon.

It is a feature of the present invention that it enables there to beproduced spherical porous carbon structures with a controlled range ofparticle size e.g. where the size distribution of the spheres can becontrolled to give a dispersion of D90/D10 of better than 10 (preferablybetter than 5) and the larger pores can be controlled from a meandiameter of 2 nm up to 50 nm (mesopores) or greater than 50 nm(macropores) and where the mean micropore diameter can be controlled tobetween 0.6 and 2 nm to give BET surface areas from 250 to 800 m²/gwithout recourse to conventional activation procedures.

The materials of the present invention can be advantageously used in awide variety of demanding applications where the high physical strengthand high attrition resistance offer special benefits. These include, butare not limited to, liquid phase catalyst supports, blood filtration andany application where the carbon is used in a fluid bed or moving bedenvironment. The large mesopores can also be advantageously utilised insystem where larger molecules are either adsorbed or grafted within thepores. These can include drug release systems, chiral supports etc.

The invention is illustrated in the following examples.

EXAMPLE 1

A reaction mixture containing 94 weight parts of phenol, 54 weight partsof paraformaldehyde (PF) (phenol to formaldehyde molar ratio 1:1.8),specified amounts of ethylene glycol (EG) pore former and concentratedsulphuric acid (SA) was heated with stirring up to specifiedcondensation temperature (paraformaldehyde dissolves completely at about60° C.) and maintained at this temperature for a specified residencetime (Table 1-1). TABLE 1-1 EG, weight SA, weight Condensation Residence# parts parts temperature, ° C. time, minutes 1 259 35.4 72 ± 1 80 2 37045 77 ± 1 120 3 259 17.0 72 ± 1 300

The resulting viscous solution was poured as a stream into 2-4 volumesof stirred preheated (110-115° C.) mineral oil containing 0.5% of adrying oil, acting as a dispersing agent. The temperature of theresulting mixture dropped to ˜100-102° C., and cross-linking occurrednormally within 1-2 minutes. The resulting slurry was gradually heatedup to 115-120° within 30-60 minutes to complete the curing and cooleddown. Resin in bead form was filtered off from the oil, washed severaltimes with hot water to remove both pore former and catalyst. Theresulting porous spherical resin, containing water, residual oil, tracesof pore former and catalyst can then be directly carbonised to producespherical porous carbon

For analysis of the resin it can be washed repeatedly with organicsolvent, preferably with ethanol-ether 1:1 v/v solution, and dried invacuo until constant weight. The pore size distribution graphs and somestructural parameters of carbonised materials, formed by heating at 800°C., in carbon dioxide flow, are given in FIG. 1 and Table 1-2. In whichthe effect of the pore former content and catalyst's concentration inthe resin composition on the porosity of derived carbonised material isshown. Reaction system Phenol—Formaldehyde—Ethylene Glycol—SulphuricAcid. TABLE 1-2 Pore Volume BET area, (P/P₀ = 0.98), Bulk Density, m²/gcm³/g g/cm³ Carbon 1.1 571.1 0.58 0.34 Carbon 1.2 598.2 0.90 0.32 Carbon1.3 475.7 0.26 0.69

EXAMPLE 2

A reaction mixture containing 94 weight parts of phenol, specifiedamounts of aniline (A), ethylene glycol pore former, paraformaldehydeand concentrated sulphuric acid was heated with stirring up to specifiedcondensation temperature (complete paraformaldehyde dissolution occursaround 60° C.) and maintained at this temperature for specifiedresidence time (see Table 2-1). TABLE 2-1 EG, PF, A, SA, weight weightweight weight Condensation Residence # parts parts parts parts temp. °C. time, min. 1 272 56.7 4.7 37.2 73 ± 1 105 2 284 59 9.3 39 73 ± 1 1153 310.5 64.8 18.6 42.4 73 ± 1 140 4 336.2 70.2 27.9 45.9 73 ± 1 180

The resulting viscous solution was poured in a stream into 2-4 volumesof stirred preheated (110-115° C.) mineral oil containing 0.5% of thedrying oil and the resin was processed further in the same way as inExample 1. The pore size distribution graphs and some structuralparameters of carbons 2.1 to 2.4 and carbon 1.1 are compared in FIG. 2and Table 2-2, in which is shown the effect of aniline content in resincomposition of the reaction system Phenol—Aniline—Formaldehyde—Ethyleneglycol—Sulphuric acid on the porosity of derived carbons. TABLE 2-2 PoreVolume BET area, (P/P₀ = 0.98), Bulk Density, m²/g cm³/g g/cm³ Carbon1.1 571.1 0.58 0.34 Carbon 2.1 526.7 0.78 0.40 Carbon 2.2 516.7 0.310.76 Carbon 2.3 441.8 0.24 0.87 Carbon 2.4 293.9 0.16 0.83

EXAMPLE 3

Industrial Novolac resin in amount of 100 weight parts was mixedtogether with specified amount of ethylene glycol pore former (see Table3-1) at elevated temperature and with stirring to enhance the formationof a clear solution, which was then cooled down to 65-70° C., wherehexamine (HA) in amount of 9 weight parts was added. The resultingstirred mixture was gradually heated at such a rate as to reach thespecified temperature in specified residence time (see Table 3-1). TABLE3-1 Ultimate pre- Condensation EG, weight EG: condensation residence #parts Novolac + HA temp., ° C. time, min. 1 109 1.00 85 30-35 2 136.31.25 90 30-35 3 163.5 1.50 100 45-50 4 190.8 1.75 102 70-75 5 218 2.00104 75-80 6 272.5 2.50 105 75-80 7 327 3.00 105 80-85 8 381.5 3.50 10680-85 9 436 4.00 107 85-90

The viscous solution was then poured in stream into 2-4 volumes ofstirred preheated (115-120° C.) mineral oil containing 0.5% of thedrying oil. The temperature of resulting emulsion dropped to 105-110°C., but on further heating cross-linking occurred at about 115-120° C.Further heating at the rate about 0.5° C. per minute up to 150° C. wasapplied to complete the curing. After cooling down the resin beads werefiltered off from the oil and washed several times with hot water toremove the pore former and small amount (less than 5% of total) of lowmolecular weight polymer. The resulting porous spherical resin,containing water, residual oil, traces of pore former and low molecularweight fraction was carbonised by heating at 800° C. in flowing carbondioxide to produce the spherical porous carbon. If the resin beads arecarbonised directly after separation from the oil, without washing, theporosity of resulting carbons decreases. For analysis the sample ofresin should be washed repeatedly with organic solvent, preferably withethanol-ether 1:1 v/v solution, and dried in vacuo until constantweight. The pore size distribution graphs and some structural parametersof both resins and carbonised materials are presented on FIGS. 3 a and 3b and Tables 3-2 and 3-3, respectively. TABLE 3-2 Pore Volume BET area,(P/P₀ = 0.98), m²/g cm³/g Resin 3.1 Non-porous Non-porous Resin 3.2Slightly porous Slightly porous Resin 3.3 98.9 0.35 Resin 3.4 118.2 0.54Resin 3.5 141.1 0.81 Resin 3.6 144.7 0.97 Resin 3.7 111.3 0.67 Resin 3.8134.9 0.76 Resin 3.9 120.0 0.66

FIG. 3 b shows the effect of the pore former in resin composition on theporosity of corresponding carbonised materials. Reaction systemNovolac—Hexamine—Ethylene Glycol for carbons 3.1 to 3.9. TABLE 3-3 PoreVolume BET area, (P/P₀ = 0.98), m²/g cm³/g Carbon 3.1 473.2 0.26 Carbon3.2 468.3 0.30 Carbon 3.3 592.2 0.48 Carbon 3.4 567.3 0.54 Carbon 3.5579.6 0.88 Carbon 3.6 525.1 1.02 Carbon 3.7 469.3 1.13 Carbon 3.8 482.00.84 Carbon 3.9 524.8 1.06

EXAMPLE 4

Industrial Novolac resin (N) in amount of 100 weight parts was mixedtogether with specified amount of ethylene glycol pore former (EG) (seeTable 4-1) at elevated temperature and on stirring to enhance theformation of clear solution, which then was cooled down to 65-70° C.where specified amounts of hexamine (HA) and modifying agent(MA)—aniline (A) or urea (U), were added. TABLE 4-1 EG, HA, A, U, EG:CT, RT, # w.p. w.p. w.p. w.p. N + HA + MA ° C. min 1 246.4 13.2 10 — 2.091 35 2 288 24 20 — 2.0 80 50 3 246.4 13.2 — 10 2.0 103 75 4 288 24 — 202.0 103 60

The resulting stirred mixture was gradually heated at such a rate as toreach the specified temperature (CT) in specified residence time (RT)(Table 4-1). Then the viscous solution was poured as a stream into 2-4volumes of stirred pre-heated (110-115° C.) mineral oil containing 0.5%of the drying oil. The temperature of the resulting emulsion dropped to100-105° C., but on further heating cross-linking occurred at about105-110° C. Further heating at a rate of about 0.5° C. per minute up to150° C. was applied to complete the curing. After cooling down the resinbeads were processed further in the same way as in Example 3. The poresize distribution graphs and some structural parameters of thecarbonised materials carbons 4.1 to 4.4 (800° C., flowing carbondioxide) are compared with those of the carbon 3.5 in FIG. 4 and Table4-2 TABLE 4-2 Pore Volume BET area, (P/P₀ = 0.98), m²/g cm³/g Carbon 3.5578.6 0.88 Carbon 4.1 612.6 0.77 Carbon 4.2 629.6 0.81 Carbon 4.3 648.10.73 Carbon 4.4 717.0 1.08

EXAMPLE 5

A clear solution of 100 weight parts of industrial Novolac resin in 327weight parts of specified pore former (see Table 5-1) was heated up to65-70° C. where 9 weight parts of hexamine were added. The resultingreaction mixture was gradually heated on stirring to reach the ultimatecondensation temperature of 105-107° C. in 75-80 minutes. TABLE 5-1 #Pore Former, weight parts PCT, ° C. RT, min 1 1,4-Butylene glycol, 327105 85 2 1,2-Propylene carbonate, 327 108 70 3 Di(ethylene glycol), 327103 90 4 Tri(ethylene glycol), 327 104 80 5 γ-Butyrolactone, 191 -Water, 11 106 60 6 Dimethylformamide, 278 - Water, 5.5 120 100 7N-Methyl-2-pyrrolidinone, 327 - Water, 5.5 122 80

Then the viscous solution was poured as a stream into 2-4 volumes ofstirred pre-heated (115-120° C.) mineral oil containing 0.5% of thedrying oil. The temperature of resulting emulsion dropped to 110-115°C., but on further heating cross-linking occurred, normally at about120° C. The further processing was the same as in Examples 3 and 4. Thepore size distribution graphs and some structural parameters ofcarbonised materials obtained by heating at 800° C., in carbon dioxideor nitrogen flow, carbons 5.1 to 5.8 are presented in FIG. 5 and Table5-2 and compared with those of carbon 3.7. TABLE 5-2 Pore Volume BETarea, (P/P₀ = 0.98) Bulk Density, m²/g cm³/g g/cm³ Carbon 3.7 469.3 1.130.30 Carbon 5.1 586.0 0.57 0.47 Carbon 5.2 621.0 0.92 0.67 Carbon 5.3556.4 0.37 0.76 Carbon 5.4 548.1 0.33 0.75 Carbon 5.5 498.5 0.27 0.73Carbon 5.6 524.2 0.28 0.33 Carbon 5.7 511.8 0.28 0.33

EXAMPLE 6

A clear solution of 100 weight parts of industrial Novolac resin and 9weight parts of hexamine in 327 weight parts of the pore former ofspecified composition (see Table 6-1) was processed exactly as inExample 5. TABLE 6-1 # Di(ethylene glycol), w.p. Ethylene glycol, w.p.Water, w.p. 1 272.5 — 54.5 2 218 — 109 3 163.5 163.5 —

The pore size distribution graphs and some structural parameters ofcarbonised materials obtained by heating at 800° C., in flowing carbondioxide are presented in FIG. 6 and Table 6-2 carbons 6.1 to 6.3 andcompared with those of carbon 5.3. TABLE 6-2 Pore Volume BET area, (P/P₀= 0.98) m²/g cm³/g Carbon 5.3 556.4 0.37 Carbon 6.1 561.2 0.39 Carbon6.2 585.0 0.38 Carbon 6.3 606.1 0.58

EXAMPLE 7

A reaction solution containing 100 weight parts of industrial Novolacresin, 12 weight parts of hexamine, 7 weight parts of anhydrouscopper(II) sulphate, 190.4 weight parts of ethylene glycol and 33.6weight parts of monoethanolamine (catalyst and pore former) wasgradually heated from 60 to 100° C. in 35-40 minutes. Then the viscoussolution was poured in a stream into stirred pre-heated (115-120° C.)mineral oil containing 0.5% of the drying oil. After the initial drop inthe resulting emulsion temperature to 110-112° C. further heating wasapplied at the rate 0.5° C. per minute up to 150° C. Normallycross-linking occurred at 115-120° C. The processing of the resin inbeads was the same as in Examples 3-6. FIG. 7 and Table 7 present poresize distributions and some structural parameters of the carbons derivedfrom this resin and containing ca. 5% weight. of finely dispersedcopper. Carbon 7.1 was prepared by heat treatment of the resin at 800°C. in flowing carbon dioxide. Carbon 7.2 was prepared by heat treatmentof the resin at 800° C. in flowing nitrogen. TABLE 7 Pore Volume BETarea, (P/P₀ = 0.98), m²/g cm³/g Carbon 7.1 479.3 0.55 Carbon 7.2 444.50.59

EXAMPLE 8

Industrial Novolac resin in amount of 100 weight parts was mixedtogether with 327 g of ethylene glycol at elevated temperature and onstirring to enhance the formation of clear solution, which then wascooled down to 65° C. where hexamine in amount of 9 weight parts wasadded. Resulting stirred mixture was briefly heated up to 70° C. just toensure dissolution of hexamine and poured in stream into 3 volumes ofstirred preheated (190° C.) mineral oil containing 0.5% of the dryingoil. The temperature of resulting emulsion dropped to 160° C., andalmost immediately (less than in 1 min) cross-linking occurred. Thetemperature of the reaction mixture was raised up to 175° C. in 15 minto complete the curing. After cooling down the resin in beads wasfiltered off from the oil and further processed in a way similar toExample 3. The pore size distribution graph and some structuralparameters of the carbon produced from the resulting resin, cross-linkedunder severe conditions, (Carbon 8, 800° C., carbon dioxide) arecompared on FIG. 8 with corresponding properties of the carbon (Carbon3-7) derived from the compositionally similar resin, but cross-linkedunder mild conditions (Example 3, 7).

EXAMPLE 9

Industrial Novolac resin in amount of 100 weight parts was mixedtogether with 236 weight parts of ethylene glycol at elevatedtemperature and on stirring to enhance the formation of clear solution,which then was cooled down to 65° C., where hexamine in amount of 3weight parts and furfural in amount of 15 weight parts were added.Resulting stirred mixture was gradually heated to reach 110° C. in 1 hr,and viscous solution was poured in stream into 3 volumes of stirredpreheated (120° C.) oil, containing 0.5% of the drying oil. On furtherheating curing occurred at 140-145° C. (in 15-20 min.). After furtherheating to complete curing (up to 155° C. in 20 min.) and cooling resinin beads was filtered off and processed as described in Examples 3-6.Porosity parameters of corresponding carbon are presented in FIG. 9.

EXAMPLE 10

Industrial Novolac resin in amount of 100 weight parts was mixedtogether with 218 weight parts of ethylene glycol at elevatedtemperature and on stirring to enhance the formation of clear solution,which then was cooled down to 65-70° C., where hexamine (HA) in amountof 9 weight parts was added. Resulting stirred mixture was graduallyheated at such a rate as to reach 95-97° C. in 70 min. Then the hotviscous solution was poured into shallow trays either made of or linedwith inert material (e.g., Pyrex™ glass or metal lined with PTFE film)that were consequently sealed to minimise the pore former loss. Trayswere put into suitable preheated (100° C.) oven. The temperature withinthe oven was gradually raised to reach 150° C. in an hour and maintainedat this level for another hour. After cooling resulting solid blocks ofresin were crashed to give particles with maximal size of 1 cm. Crushedresin was washed several times with hot water and dried at 80-100° C. onair. Dry resin could be milled, classified and carbonised in a normalway to produce mesoporous carbon of desired particle size but irregularshape of particles. If the resin is carbonised directly after crashingwithout washing, the mesoporosity of resulting carbon decreasesessentially. The pore size distribution graphs and some structuralparameters of both resin and carbonised material (800° C., carbondioxide flow) are presented in FIG. 10. Similar procedures could beapplied for the preparation in blocks of all the other resins of theinvention.

EXAMPLE 11

Reaction solution consisting of 100 weight parts of industrial Novolacresin, 9 weight parts of hexamine, 20 weight parts of boric acid and 258weight parts of ethylene glycol was heated up from 70 to 100° C. in 45min. Resulting viscous solution was poured in stream into 3 volumes ofstirred preheated (105° C.) oil, containing 0.5% of the drying oil. Onfurther heating curing occurred at around 110° C. Further heating wasapplied up to 160° C. in 30 min. to complete the curing. After filteringthe resin beads off further treatment prior to carbonisation was appliedin three different ways:

1.—No treatment at all.

2.—Several washings with hot water.

3.—Extraction with ether in Soxhlett apparatus.

Pore size distribution graphs of the resulting carbons 11.1 to 11.3 andother parameters are compared in FIG. 11 and Table 11. TABLE 11 Porevolume BET area, (P/Po = 0.98), B₂O₃ Bulk Density, m²/g cm³/g content, %g/cm³ Carbon 11.1 303.1 0.41 6.8 0.47 Carbon 11.2 410.0 0.79 5.3 0.36Carbon 11.3 346.3 0.57 6.6 0.38

EXAMPLE 12

A solution containing 100 weight parts of industrial Novolac resin (N),194.4 weight parts of clear solution made of 27.54 weight parts ofMelamine (M), 26.18 weight parts of Paraformaldehyde (PF) and 140.68weight parts of Ethylene Glycol (EG), and additionally—specified amountof Ethylene Glycol (EG) (Table 12-1) was placed into glass tray, sealed,put into preheated oven and kept at 140±5° C. for 15 hours, thoughgelatin occurs within first 2-3 hours. After cooling down the resin inblock was further processed as in Example 10. The pore size distributiongraphs and some structural parameters of both resins and carbonizedmaterials (800° C., carbon dioxide flow) are presented in FIG. 12 a, 12b and Table 12-2. TABLE 12-1 Additional EG, Gelation time, # weightparts Σ EG/(N + M + PF) hrs 1 89.85 1.5 2.00 2 243.55 2.5 2.50 3 320.403.0 2.75 4 474.10 4.0 3.00

TABLE 12-2 Pore Volume BET area, (P/Po = 0.98), m²/g cm³/g Resin 12.1Non-porous Non-porous Resin 12.2 193.9 0.41 Resin 12.3 202.4 0.38 Resin12.4 120.9 0.24 Carbon 12.1 436.2 0.24 Carbon 12.2 608.8 0.53 Carbon12.3 612.8 0.77 Carbon 12.4 577.4 0.49

EXAMPLE 13

Industrial Novolac resin (N) in amount of 100 weight parts was dissolvedin specified amount of Ethylene Glycol (EG). The solution of 10 weightparts of Resorcinol (R) or Hydroquinone (Hq) in 30 weight parts of EGwas added to the Novolac solution together with 12 weight parts ofHexamine (HA). Resulting reaction solution was heated up to a specifiedtemperature for a specified time (Table 13-1), poured into a stirred hotoil (120° C.) containing 0.5% of the drying oil and processed further asdescribed in Examples 3-6. Properties of the carbons derived from theresins thus obtained are compared with the properties of carbons 3.2 and3.4 in FIG. 13 and Table 13-2. TABLE 13-1 EG, R, Hq, Σ EGUltimate solution temp., ° C. # weight parts weight parts weight partsN + HA + R(Hq) Residence time, min. 1 122.5 10 — 1.25  90/40 2 183.5 —10 1.75 103/60

TABLE 13-2 Pore Volume BET area, (P/Po = 0.98), m²/g cm³/g Carbon 3.2468.3 0.30 Carbon 3.4 567.3 0.54 Carbon 13.1 754.9 0.57 Carbon 13.2676.1 0.94

1. Mesoporous carbon having a pore structure that, as estimated bynitrogen adsorption porosimetry, comprises (a) micropores of diameter ofup to 20 A; and (b) mesopores of diameter of 20-500 A wherein the valuefor the differential of pore volume V with respect to the logarithm ofpore radius R (dV/dlogR) for the mesopores is greater than 0.2 for atleast some values of pore size in the range 20-500 A.
 2. The carbon ofclaim 1, wherein the value for the differential of pore volume V withrespect to the logarithm of pore radius R (dV/dlogR) for the mesoporesis greater than 0.25 for at least some values of pore size in the range20-500 A.
 3. The carbon of claim 1, wherein the value for thedifferential of pore volume V with respect to the logarithm of poreradius R (dV/dlogR) for the mesopores is greater than 0.3 for at leastsome values of pore size in the range 20-500 A.
 4. The carbon of claim1, wherein the value for the differential of pore volume V with respectto the logarithm of pore radius R (dV/dlogR) for the mesopores isgreater than 0.4 for at least some values of pore size in the range20-500 A.
 5. The carbon of claim 1, wherein the value for thedifferential of pore volume V with respect to the logarithm of poreradius R (dV/dlogR) for the mesopores is greater than 0.5 for at leastsome values of pore size in the range 20-500 A.
 6. The carbon of claim1, wherein the distribution of mesopores and macropores is bimodal overa size range of 10-1000 Å.
 7. The carbon of claim 1, further comprisingmacropores of diameter above 500 Å observable by the differential ofpore volume V with respect to the logarithm of pore radius R (dV/dlogR)having a value above 0.2 for pores of size 500 Å.
 8. The carbon of claim1, further comprising macropores of diameter above 500 Å observable bythe differential of pore volume V with respect to the logarithm of poreradius R (dV/dlogR) having a value above 0.3 for pores of size 500 Å. 9.The carbon of claim 1, further comprising macropores of diameter above500 Å observable by the differential of pore volume V with respect tothe logarithm of pore radius R (dV/dlogR) having a value above 0.4 forpores of size 500 Å.
 10. The carbon of claim 1, further comprisingmacropores of diameter above 500 Å observable by the differential ofpore volume V with respect to the logarithm of pore radius R (dV/dlogR)having a value above 0.2 for pores of size 500 Å.
 11. The carbon ofclaim 1, which has a BET surface area of 250 to 800 m² per gram.
 12. Thecarbon of claim 1, which is in the form of a powder.
 13. The carbon ofclaim 1, which is in the form of beads of diameter of 2 to 1600 μm. 14.The carbon of claim 1, which is activated.
 15. The carbon of claim 1,which is substantially uncontaminated by sulfur.
 16. The carbon of claim1 which is the product of carbonizing a cured phenolic resin.